Photoelectron spectroscopy reveals molecular diffusion through physisorbed template layers on Au(111)

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Molecular exchange processes in organic heterostructures are often detrimental to the performance of nano-optoelectronic devices. Bilayers of vacuum sublimed organic semiconductors on inorganic substrates can serve as reductionist model for organic–organic interfaces and the coupling strength of the template layer on the substrate is a decisive factor for possible molecular exchange. We use density-functional theory modelling and x-ray photoelectron spectroscopy to show that the coupling of the pentacene oxo-derivatives 6,13-pentacenequinone (P2O) and 5,7,12,14-pentacenetetrone (P4O) with Au(111) is weak. Consequently, as shown by ultraviolet photoelectron spectroscopy, subsequently deposited copper-phthalocyanine (CuPc) diffuses through the template layers to the Au(111) substrate.